The present invention relates to an automatic process and apparatus for producing a lock nut, and more particularly relates to automatization in production of a lock nut used for fastening purposes in cooperation with a bolt.
In the conventional production system of such a lock nut, a tubular material of a hexagonal transverse cross section is machined to form a block which is made up of a main body of the ordinary nut configuration and a truncated cone axially integral with one end of the main body. The main body and the truncated cone have a common through, axial center hole. Next, a plurality of, for example six, radial slits are formed at equal center angle intervals in the wall of the center hole in the region of the truncated cone. Then, the center hole is machined by, for example, a thread grinder to form it into a tapped hole. Finally, the truncated cone of the block is mechanically squeezed inwards by compressing in the axial direction with a mould having a truncated, conical recess. This compression minimized the diameter of the tapped hole in the region of the truncated cone in obtain an intended lock nut.
In the case of this conventional production system, presence of the slits formation step forms a serious neck in full automatization of the process, because the slit formation step requires a great deal of manual labour. Obviously, need for such manual labour causes undesirable increase in production cost. Presence of slit formation induces another problem in use of the lock nut. Formation of such slits develops sharp points at the squeezed end of each slit and the slits tend to damage the threaded surface of an associated bolt in screw engagement with the lock nut, thereby producing fine metallic chips. Presence of such fine metallic chips between the lock nut and the bolt are liable to cause serious seizure in the screw engagement.
In addition to the problem of damage on an associated bolt, it is also important in design of a lock nut to assure reliable fastening on the bolt. In order to suffice this requirement, it is necessary to provide the lock nut with an elastic construction which applies elastic fastening on the bolt in screw engagement with the lock nut. No special consideration is paid in this regard in production of lock nuts.